1. Field of the Invention
The field of the invention relates generally to echogenic surfaces, and more particularly, to echogenic surfaces for medical instruments, e.g., needles used in medical procedures, to enhance the ultrasonic visibility of the medical instruments.
2. Background
Needles are commonly used in various medical procedures, such as biopsy and amniocentesis procedures, to gain percutaneous access into the body. In a biopsy, for example, a biopsy needle is inserted into the body to collect a tissue sample from a tumor. In amniocentesis, an aspiration needle is inserted into the amniotic sac to collect amniotic fluid.
These medical procedures are frequently monitored using an imaging technique. One widely used imaging technique is ultrasonography, which is commonly used to image the development of a fetus. Ultrasonography relies on the “echogenicity” or ultrasonic visibility of organs and bones, and medical instruments placed inside the body. In a biopsy, ultrasonography is used to guide the biopsy needle to the tumor site. In amniocentesis, ultrasonography is used to guide the aspiration needle inside the amniotic sac to avoid injury to the fetus.
In order to guide a needle inside the body using ultrasonography, the needle must be visible in an ultrasound image. Unfortunately, the smooth cylindrical surface of a needle is very difficult to image using ultrasonography. FIG. 1 illustrates a medical device 20 (e.g., a needle) of the prior art shows ultrasound waves 10 emitted from a transducer 15 striking the surface of the device 20. The device 20 reflects the ultrasound waves 10 in a direction 25 away from the transducer 15. As a result, the emitted ultrasound waves 10 are not returned to the transducer 15 and the device 20 is not imaged.
To address this problem, various methods have been developed to enhance the “echogenicity” or ultrasonic visibility of a medical device, which problem can be worse for a thin device such as a needle. These methods typically involve providing a disrupted surface at the distal end or tip of the medical device or needle to enhance its ultrasonic visibility. Current methods for providing disrupted surfaces on a needle include forming rings around the outer and/or inner cannula of the needle, sandblasting the needle surface, chemically etching the needle surface, drilling holes through the cannula of the needle, and coating the needle surface with a polymeric coating. The resulting disrupted surfaces enhance the ultrasonic visibility of the needle by isotropically scattering incident ultrasonic waves. FIG. 2 illustrates an example of a prior art needle 30 with a disrupted surface 35 at its distal end. FIG. 2 shows ultrasound waves 10 emitted from a transducer 15 striking the disrupted surface 35 of the needle 30. The disrupted surface 35 reflects the ultrasound waves 10 in random directions 40 with some of the waves being reflected back to the transducer 15 and some of the waves being reflected away from the transducer 15. The reflected waves received by the transducer 15 are used to create an ultrasound image of the needle.
Another method to enhance the ultrasonic visibility of a needle is to form dimples on the needle surface. FIG. 3A illustrates a side view of a prior art needle 50 with dimples 55 formed along its surface. FIG. 3B shows a radial cross sectional view of the prior art needle 50 of FIG. 3A. FIG. 3B shows ultrasound waves 65 striking one of the dimples 55 from a transducer 60. The dimples 55 reflect the ultrasound waves in different directions 70 with some of the waves being reflected back to the transducer 60 to form an ultrasound image and some of the waves being reflected away from the transducer 60.
Although the usefulness of etched, coated and sandblasted surfaces has been demonstrated, these disrupted surfaces typically have random disruptions that scatter incident ultrasound waves with no real direction. In addition, the dimples 55 only direct ultrasound waves that are reflected off of a single point on its surface back to the transducer. The rest of the ultrasound waves are directed away from the transducer.
Therefore, there is a need for an echogenic surface that reflects more of the ultrasound waves back to the transducer. Such an echogenic surface would provide improved ultrasonic visibility of medical instruments, such as needles. This would make it easier for physicians to guide the medical instruments inside the body using ultrasonography.